Homoeologue expression insights into the basis of growth heterosis at the intersection of ploidy and hybridity in Cyprinidae (Carassius auratus red var. × Cyprinus carpio)

Abstract

Hybridization and polyploidization are considered important driving forces that form new epigenetic regulations. To study the changing patterns of expression accompanying hybridization and polyploidization, we used RNA-seq and qPCR to investigate global expression and homoeologue expression in diploid and allotetraploid hybrids of Carassius auratus red var. ([female]) (R) and Cyprinus carpio ([male]) (C). By comparing the relative expression levels between the hybrids and their parents, we defined the expression level dominance (ELD) and homoeologue expression bias (HEB) in liver tissue. The results showed that polyploidization contributed to the conversion of homoeologue ELD. In addition, hybridization had more effect on the change in HEB than polyploidization, while polyploidization has been considered to have more effect on the change of global gene expression than hybridization. Meanwhile, similar expression patterns were found in growth-related genes. The results suggested that hybridization and polyploidization result in differential degrees of maternal HEB in the three tissues tested. The results of this study will increase our understanding of the underlying regulation mechanism of rapid growth in diploid hybrids and allotetraploids. The differential degrees of global expression and homoeologue expression contribute to growth heterosis in newly formed hybrids and allotetraploids, ensuring the on-going success of allopolyploid speciation.